Define a variable in a middleware available to the following ones

Question

I am using asp.net core, and I would like to get several data from the request before I call the full web app.

So I created a middleware to do this. I found a way to check everything I want, but I don't know how to pass a variable to the following middlewares

app.Use(async (context, next) => {
    var requestInfo = GetRequestInfo(context.Request);
    if(requestInfo == null)
    {
        context.Response.StatusCode = 404;
        return;
    }

    // How do I make the request info available to the following middlewares ?

    await next();
});

app.Run(async (context) =>
{
    // var requestInfo =  ???
    await context.Response.WriteAsync("Hello World! - " + env.EnvironmentName);
});

Is there a good way to pass data from a middleware to others ? (here I use app.Run, but I would like to have all this in MVC)

Answer 1

Beside features, there is another - a simpler in my opinion - solution: HttpContext.Items, as described here. According to the docs, it is especially designed to store data for the scope of a single request.

Your implementation would look like this:

// Set data:
context.Items["RequestInfo"] = requestInfo;

// Read data:
var requestInfo = (RequestInfo)context.Items["RequestInfo"];

Answer 2

I found the solution : the context contains an IFeatureCollection, and it is documented here

We just need to create a class with all the data :

public class RequestInfo
{
    public String Info1 { get; set; }
    public int Info2 { get; set; }
}

And we add it to the context.Features :

app.Use(async (context, next) => {
    RequestInfo requestInfo = GetRequestInfo(context.Request);
    if(requestInfo == null)
    {
        context.Response.StatusCode = 404;
        return;
    }

    // We add it to the Features collection
    context.Features.Set(requestInfo)

    await next();
});

Now it is available to the others middlewares :

app.Run(async (context) =>
{
    var requestInfo = context.Features.Get<RequestInfo>();
});